Sound film printing optical system



1945. J. A. MAURER, JR 2,381,979

- I SOUND FILM PRINTING OPTICAL SYSTEM Filed Aug. 28, 1943 4Sheets-Sheet 1 Fly-3 /v r 1 102 Q95 3a' 5 t 2 32 I 5 s i 7 P INVENTOR:Jobn A. Mauren/x: w emaau Aug. 14, 1945. J. A. MAU RER, JR

SOUND FILM PRINTING OPTICAL SYSTEM Filed Aug. 28, 1943 4 Sheets-Sheet 2IN V EN TOR.

r. i W MWA A W 0 f B J. A. MAURER, JR

SOUND FILM PRINTING OPTICAL SYSTEM Filed Aug. 28, 1943 4 Sheets-sheaf 3lOQa.

INVENTOR:

Jo/m A. MauregJr:

i- J. A. MAURER, JR 2,381,979

SOUND FILM PRINTING OPTICAL SYSTEM FiledAugQZS. 1943 4 Sheets-Sheet 4Ffy. /4

I I 1 I I I IN VEN TOR.

AGE/VT Patented Aug 14, 1945 SOUND PRINTING OPTICAL SYSTEM John A.Maurer, Jr., New York, N. Y., asslgnor to J. A. Maurer, Inc., New York,N. Y., a corporation of New York Application August 28, 1943, Serial No.500,393

14 Claims.

This invention relates to opticalsystems for sound track printers and,more particularly, it"

relates to optical'systems of this kind by which a variable area soundtrack may be converted into a variable density sound track.

Still more particularly, the invention relates to sound printing-opticalsystems in which the conversion of the variable area. sound track intothe variable density sound track is effected substantially as follows.First, a uniformly illuminated light spot is formed in such a mannerthat it ismore. or less obscured when a negative film having thevariable area sound track thereonmoves vertically through a plane atright angles to the optical axis of the system. Then, the light fluxemanating from the uniformly illuminated light spot is, inthe'verticalplane, forcused at a position in the optical system while,in the hori zontal plane, it is diffused at .that position. Thus, thereis formed at that position an image of the uniformly illuminated lightspot as obscured by the variable area sound track, which image is alight spot ofvertically varying, illumination. Finally, the light fluxemanating from the light spot of vertically varying illumination isemployed to effect the exposure of a positive film which movesverticallythrough another plane at right angles to the optical axis of the system,and thereby the variable density sound track is produced on the positivefilm.

Conversion sound printing optical systems of this type are disclosed,for example, in Sandvik et al. Patent No. 2,298,422, issued October 13,1942, and in my copending applications Serial Nos. 449,797, now PatentNumber 2,366,040 issued December 26, 1944, and 449,798, filed July 4,1942, and assigned to the same assignee as this application. In all ofthose opticalsystems the uni- I formly illuminated light spot is of arectangular shape so as to have two straight and parallel horizontaledges. The distance from one another of the horizontal edges of theuniformly illuminated light spot, that is, its vertical extension, orheight, therefore is constant at all points on the horizontal edges.This shape of the uniformly illuminated light spot results in a linearrelationship between the exposure of the positive film and thehorizontal extension, or width of the transparent portion of thevariable area sound track, whose opaque portion more orless obscures theuniformly illuminated light spot.

The light transmissionof a developed film, however, is not linearlyrelated to its exposure.

(or. sat-24) Thus, since in the conversion sound printing opticalsystems of 2,366,040 and application Serial No. 449,798 the exposure ofthe positive film is linearly related to the width of the transparentportion of the variable area sound track, the light transmission of thevariable density sound track will not be linearly related thereto afterthe positive film has been developed. Distortions, therefore, would 10,occur if sound were reproduced directly from the variable densitysoundtrack on the developed positive film. For that reason, it has beennecessary heretofore to transfer the variable density sound track fromthe positive film onto another 16 film by a further printing operation.For the same reason, 'it furthermore has been necessary to employ, asthe positive film and the film onto which the further print of thevariable density sound track was made, only those kinds of film 20 stockwhose emulsion characteristics approach linearity over' as wide a rangeas possible and, moreover, to employ them in such a manner thateffective use was made of only the straight portions of their emulsioncharacteristics. The first 26 of these requirements excludes theemployment of a number of film stocks now available which, except fortheir emulsion characteristics, would make excellent sound trackcarriers,- and the second requirement results in an objectionable 30restriction of the volume range of the sound reproduced from the finalprint of the variable density sound track.

For the purpose, therefore; of producing on the positive film a variabledensity sound track from 5 which undistorted sound can be reproduceddirectly, and/or for the purpose of making possible the employment,without causing distortions on account of the non-linearity of itsemulsion characteristic, of any kind of film stock as the posi- 40 tivefilm and; if desired,- the film onto which a further print of thevariable density sound track is made, and/or for the purpose ofeffectively enhancing the volume range of the reproduced sound, it isdesirable to establish, in the conversion sound printing opticalsystems'of the type under discussion, a non-linear relationship betweenthe width of the transparent portion of the variable area sound trackand the exposure of the positive film so as to compensate for the sonon-linearity of the emulsion characteristic of either the positive filmor both the positive film and the film onto which the variable densitysound track is to be printed from the positive film. That is to say, thenon-linear relationship must be of such a character that a linearrelation- Patent Nos. 2,298,422 and ship is established between saidwidth and the light transmission of the variable density sound trackafter the film, or films. have been developed. This compensatingnon-linear relationship, however, is merely an example of a non-linearrelationshipwhich it is desirable'to establish, in the conversion soundprinting optical systems of the type'under discussion, be-

- quirements of a given actual case.

a It will readily be understood by those skilled in the art that themeans for establishing nonlinear relationships of thekind described inthe preceding paragraph preferably are such that they may convenientlybe introduced into the optical systems of the type under discussion, and

that they may be manufacturemwith comparative ease and yet with anydesired degree of accuracy.

It is, therefore, the primary object of the invention to provide,.inconversion sound printing optical systems of the type under discussion,

means for establishing a non-linear relationship between thewidth of thetransparent. portion of the variable area sound track and the exposureof the positive film.

A further object of the invention is to provide,

in those optical systems, means for establishing a non-linearrelationship between said width and said exposure which is of a seconddegree character.

Another object of the invention is to provide." in

those optical systems, means for establishing a non-linear relationshipbetween said width and said exposure which is of a third degreecharacter. u I

Another object of the invention is to provide,

in those optical systems. means for establishing a non-linearrelationship between said width and said exposure which is of a complexcharacter.

Another object of the invention is to provide,

in those optical systems, means for-establishing .a non-linearrelationship between the width of the transparent portion of thevariable area sound track' and the exposure of the positive film whichis ofsuch a character that .a linear relationship is established betweensaid width and the light transmission of the variable density soundtrack after the positive filmhas been developed.

Another object of the invention is to provide,

in those optical systems, meansfor establishing a non-linearrelationship between the width of the transparent portion of thevariable area sound track and the exposure of the positive film which isof such a character that a linear relationship is established betweensaid width and the light transmission of the variable density soundtrack after development of a film onto which the variable density soundtrack has been 7 printed from the positive film.

Another object ofthe invention is the provision Another object of theinvention is the provision of such means which may easily bemanufactured.

Another object of the invention is the provision of such means which maybe manufactured with any degree of accuracy.

Another object of the invention is the provision, in conversion soundprinting optical systems of the type under discussion, of means makingpossible the employment, as carrier of the variable density sound track,of any kind of film stock irrespective of its emulsion characteristicand without causing distortions resulting from thenon-linearity thereof.

Another object ofthe invention is the provision, in those opticalsystems, of means by which the volume range of the sound reproduced fromthe developed variable density sound track is effectively enhanced.

Another object of the invention is the provision of conversion soundprinting optical systems in which a variable density sound track isproduced from which undistorted sound can be reproduced directly. I

Still other objects and advantages of the invention include those whichare hereinafter stated or apparent, or which are incidental to theinvention.

The objects of the invention are substantially achieved by providing, inconversion sound printing optical systems of the type under discussion,means for defining the shape of the uniformly illuminated light spotreferred to hereinabove in such a manner that the exposure of thepositive film is non-linearly related to the width of the transparentportion of the variable area sound track. To that end, the shape of theuniformly illuminated light spot is defined that the light spot has twohorizontal edges and that its height.

40 that is, the distance of its horizontal edges from one another,varies. As will be explained in detail hereinafter, the law governingthe variation of the height of the uniformly illuminated light spot canbe chosen so that a non-linear relationship of any desired character maybe established between said width and said exposure. In the presentlypreferred embodiments of the invention, the means defining the shape ofthe uni-' iormly illuminated light spot include a screen with an openingwhos outline corresponds to the desired shapeof the uniformlyilluminated light spot. This screen and opening may take the place of ascreen and opening ordinarily employed in theprinting optical system, orthey may be additional thereto, as will be pointed out hereinafter.

In the foregoing brief explanation of the state of the art and summaryof the invention, and

throughout the present specification. the terms "vertical," "verticaldirection, and "vertical plane," and horizon-tel," "horizontaldirection," and "horizontal plane," and the term "coordinate planes."are used as defined in Pat- I ent No. 2,366,040. and application SerialNo.

of means for establishing non-linear relatlon I 449,798, to whichdefinitions reference is therefore made. Reference is also made to thedefinitions contained in those applications of the terms "negative film"and "positive film, and "plane of a the negative film and "plane of thepositive film," which terms are used throughout this specification asdefined in those applications.

. Furthermore, the term "variable area sound track? is used throughoutthis specification as including the two kinds of variable area soundtrack in the art as unilateral'and bilateral, or

symmetrical, variable area sound tracks. Wherever it seemed necessary todistinguish between I these two kinds of variable area sound tracks,

this has been done by expressly referring to a unilateral or asymmetrical variable area sound track. In any case, the term alsoincludes any noiseless variable area sound tracks, be they produced bythe bias, or by the shutter, noiseless method.

Finally, the term illuminatio is used throughout this specification asreferring to. the.

amount of light flux per unit area. The descrip- .tion, for example, ofa light; spot as being of uniform illumination means that the light fluxcontained in the light spot is distributed over its area in such amanner that the amounts of light flux at any two points thereon areequal. Correspondingly, the description of a light spot as being ofvertically varying illumination. means that the light flux contained inthe light spot is distributed over its area in such a manner that theamounts of light flux at any two points thereon which are on differenthorizontal levels thereof, are, in general, different.

The invention will be better understood when the following descriptionis considered with the accompanying drawings of several presentlypreferred embodiments thereof, and its scope will be pointed out in theappended claims.

In the drawings:

Fig. 1 is a diagrammatic longitudinal section in the vertical plane of aconversion sound printing optical system to which the present inventionis applicable.

Fig. 2 is a corresponding section in the horizontal plane.

Fig. 3 is an. elevation of a screen with an opening shown in Figs. 1 and2.

Fig. 4 is an enlarged elevation of the negative film having thereon aunilateral variable area sound track and the uniformly illuminated lightspot formed in its plane when the screen and opening of Fig. 3 areemployed in the optical system of Figs. 1 and 2.

Fig. 5 is an enlarged elevation of a part of the optical system of Figs-1 and 2, showing the light spot of vertically varying illuminationformed therein in the plane of the positive film. and the variabledensity sound track produced on the positive film. 1

Fig. 6 is an enlarged elevation of the negative film having thereon thebeginning of a unilate al variable area sound track and the uniformlyilluminatedlight spot formed in its plane by means of the screen andopening of Fig. 3; certain relationsbetween the transparent portion ofthe sound track and the light spot being indicated in a diagrammaticmanner.

Fig. '7 is an enlarged elevation of a uniformly illuminated light spotembodying the invention and having such a shape that the exposure of t epositive film is a second degree function of the width of thetransparent portion of the variable area sound track.

Fig. 7A shows amodification of the uniformly illuminated light spot ofFig. 7.

Fig. 8 is an enlarged elevation of a uniformly illuminated light spotembodying the invention and having such a. shape that said exposure is athird degree function of said width.

Fig. 8A shows a modificat'ion of the uniformly illuminated light spot ofFig. 8.

Fig. 9 is an enlarged elevation of the negative film having thereon thebeginning of a unilateral variable area sound. track anda uniformlyilluminated light spot embodying the invention and being shaped so thatthe non-linear relationship between said width and saidexposure is ofsuch a character that the light transmission. of

the variable density sound track. produced on the positive film is,after development thereof,

linearly related to said width; certain relations track of the uniformlyilluminated light spot of Fig. 7; certain relations between thetransparent portion of the sound track and the light spot beingindicated in a diagrammatic manner.

Fig. 11B is an enlarged elevation of the negative film having thereonthe beginning of another type of symmetrical variable area sound trackand an adaptation for use with this type of sound track of the uniformlyilluminated-light spot of Fig. 7 certain relations between thetransparent portion of the sound track and the light spot beingindicated in a diagrammatic manner.

Fig. 12 shows an adaptation of the uniformly illuminated light spot ofFig. 8 for use with the two types of symmetrical variable area soundtracks shown in Figs. 11A and 11B, respectively.

Fig. 13 shows an adaptation for the same purpose of the uniformlyilluminated light spot of Fig. 7A.

Fig. 14 shows an adaptation for the same purpose of the uniformlyilluminated light spot of 3 Fig. 8A.

Fig.15A shows an adaptation of the uniformly illuminated light spot ofFig. 9 for use with the type of symmetrical variable area. sound trackof Fig. 3 with an open ng whose outline corresponds to the shape of theuniformly illuminated light spot of Fig. 7.

Fig. 18 is an elevation of an additional screen with an opening whoseoutline corresponds to the shape of the uniformly illuminated l ght spotof Fig. 7.

Fig. 19 is a diagrammatic longitudinal section of a part of the opticalsystem of Figs. 1 and 2 showing how the screen of Fig. 18 may be placedtherein.

In Figs. 1 and 2, there is shown by way of example one of the conversionsound printing optical systems disclosed in application Serial No.

449,798. Figs. 1 and 2 of this application are identical with Figs. 1and 2 of applicationserial No. 449,798, and Figs. 3 to 5 of thisapplication which relate to certain parts of the optical sys-' tem ofFigs. 1 and 2, are identical with Figs. 3 to 5 of application Serial No.449,798. Like parts are therefore designated by like referencecharacters in the two applications. Reference is made to the detailedexplanation given in application Serial No. 449,798 of the manner inwhich the 4 v y conversion, by printing, of a variable area'sound Itrack into a variable density sound track is effected in the opticalsystem of Figs. 1 and 2. This the horizontal levels of light spot ll.

longer ones.

explanation maybe recapitulated for the purpose of this specification asfollows: 7

As has already been pointed out hereinabove,

the conversion effected in the optical system of Figs. 1 and 2-involvesfirst the formation therein of a uniformly illuminated light spotin'such a manner that it is ore or less obscured when a 'negativefilmhaving the variable area sound track thereon moves vertically through aplane at right angles to the optical axis of the system. In the exampleillustrated, the uniformly illuminated light spot is light spot I! (Fig.4) which is formed through its plane, as indicated in Fig. 1 by thearrow 22, and hence is more or less obscured by the opaque portion ofsound track S (Fig. 4).

Light spotll as obscured by the opaque portion ofsound track S is imagedin the plane of the positive film P by the cylindrical lens 30 whosecylinder axis is horizontal, and which hence acts in only the verticalplane. Since, furthermore, cylindrical lens so is the only imaging meansin the optical system of Figs. 1. and 2 having at its conjugate focilight spot I! and the portion of sound track 8, and the variation inillumination of light spot 3| is a. linear function of the variation inwidth of the transparent portion of sound track S. The light fiuxemanating from light spot 3| effects the exposure of film P when film Pmoves vertically through its plane in the direction of the arrow 23, andthus there is produced on film P a sound track 28 which is of thevariable density type but has otherwise the same characteristics as thevariable area sound track S on film N (Fig. 5)

on the basis of the foregoing description of the imagery performedbetween the planes of films N and P, and with reference to Fig. 6 of athis application, it shall now be explained in more detail how theexposure of film P is effected in the optical system of Figs. 1 and .2.In Fig. 6, there is again shown the negative film N having thereon thebeginning of the variable area sound track S with its opaque portionO-and its transparent portion T. The vertical edges I02 and III! ofsound track S constitute the straight boundaries of portions T and 0,respectively, which portions are separated by the undulating boundplaneof film P, respectively, the light flux emanating from light spot I! istreated differently in the two co ordinate planes: In the verticalplane, the light fiux is focused by cylindrical lens 20 at the plane offilm P while, in the horizontal plane, it Ispermitted to diverge so thatit is diiIused at that position (Figs. 1 and 2).

More particularly, light spot I! as obscured by the opaqueportion ofsound track S may be considered as being composed of a large number ofhorizontal levels whose illumination is uniform. These horizontal levelsare equal in their very small vertical extension, or height, but vary inhorizontal extension, or length, in accordance with the variation inwidth of the transparent portion of sound track S. The horizontal levelsof light spot II are imaged in the plane of film P by the action ofcylindrical lens III in the vertical plane, and thusa correspondinghorizontal level is formed in the plane of film P for each of But,because of their divergence in the horizontal plane,

the light fiuxes contained in the individual horiof film P. Thehorizontal levels formed in the out over any one horizontal level in theplane I of film P is substantially equal to the amount of light fluxcontained in the corresponding level of light spot l1. Those horizontallevels in the' plane of film P which are images of the shorter levels oflight spot I! consequently have less il lumination than those which areimages of the The horizontal levels in the plane of film P thus,constitute a light spot 3| of vertically varying illumination (Fi 5).Light spot Ii is the ary Hi5.

rectangular light spot I! which is formed in the plane of film N asexplained hereinabove. The disposition of light spot ll with respect tosound track S is such that its vertical edge 82 is in alignment with thestraight boundary I02 of portion T, and its horizontal edge 64 parallelto horizontal edge I04 of sound track S. When, therefore, film N movesthrough its plane in the direction indicated by the arrow 22, light spotI! is more or less obscured .by portion 0 or, in other words, theamountof the light flux from lamp filament In transmitted by portion T towardscylindrical lens ill and film P, is varied in accordance with thevariation in width of portion T.

Portion T may be considered as being composed of a large number oftransparent levelswhich are of very small'and equal height butvaryinglength, the length of any one transparent level being equal tothe width. of portion T at the position of the transparent level. Thetransparent levels extend horizontally between'the straight boundary ID:of portion T and its un-. dulating boundary I05, and thus are parallelto horizontal edge ills of sound track 8 and horizontal edges ti and 64of light spot ll. One such transparentlevel is indicated, by way ofexample, at I06 in Fig. 6. Level I06 extends from a point on boundaryIM-to a point III! on boundary I05. As film N moves in the direction ofthe arrow 22, level Hi6 traverses light spot l'l from its horizontaledge. 6| to its horizontal edge .64. Thus, level I06 sweeps out theportion A of light spot il between its vertical edge 82 and the brokenvertical line I08 through point ill, thereby transmitting an amount oflight flux which is a linear function of the area of portion A.

Let it now be assumed that, while film N moves in the direction of thearrow 22, film P moves in the direction of the arrow 23 (Fig. 1).According to well known lawsoi' optics, a certain horizontal level 206(not shown) on film P then is, in the vertical plane, conjugate to levelI" while level I 08 traverses light spot. II. On account of theparticular imagery performed in the optical system of Figs. 1 and 2 andexplained hereinabove, the amount of light flux pread out over level208,15, during any fraction of the time in- Likewise on film N, andbelow sound track S, there is shown the uniformly illuminated va,sa1,e7e -which level I08 traverses light snot II, substantially equalto the amount of light flux transmitted at this instant by level I08.The exposure of, that is, the total amount of light flux received by,film P at level 208 therefore is substantially equal to the amountv oflight flux transmitted by level I06 duringthe total time in which ittraverses light spot I1. Since, as has been pointed out in the precedingparagraph, the amount of light flux transmitted by level I08 is a linearfunction of the area of portion A, the exposure of level 208 thus islikewise a linear function of the area of portion A.

While they have been made with reference to x the rectangular light spotII'shown in Figs. 4

and 6, the above explanations are valid for any shape the uniformlyilluminated light spot in the plane of film N may assume.- In the caseof rectangular light spot 'II, however, these further considerationsapply:

Portion A is defined by vertical edge 82 of light .spot I! and by thesection I08 of vertical line I08 which is within light spot II. PortionA is further defined by the sections 66 and 88 of hori zontal edges 6|and 64, respectively, of light spot II, which sections are between edge82 and line I08. Since light spot I! is a rectangle, edges 6I and 84both are perpendicular to edge 62 and hence parallel to one another.Since, furthermore, edges 8| and 64 are parallel to horizontal edge I04of sound track S, vertical line I08 is perpendicular to edges 6| and 84.Portion A thus is a rectangle whose one side is of the length w of levelI06, while its other side is of the length ,h of section I03, and whosearea hence is a function of the product wx'h. Moreover, on account ofthe rectangular shape of light spot I! its height, that is, the distanceof horizontal edges 6| and 64 from one another, is constant at allpoints thereon. For that reason, the value of h remains constant nomatter atwhat distance from vertical edge I02 of sound track S, andvertical edge 62 of light spot I1, vertical llnell8 is drawn throughpoint I01, the distance of line- I08 from edge I02 being,'of course,equal to the length w of level I06. In the case of rectangular lightspot II, therefore, the factor w is the only variable of the two factorsto whose product the area of portion A is related. Hence, the area ofportion A is in this case a linear function of w and, since it is such afunction, the exposure of level 208 is, for the reasons set forthhereinabove,

also a linear function of w.

Let it now be assumed that, in place of the uniformly illuminatedrectangular light spot I], there is formed in the plane of film N auniformly illuminated light spot X (not shown), and that the shape oflight spot x is deilned so that light spot X has two horizontal edgesand that its height,-that is, the distance of its horizontal edges fromone another, varies. The length I: of the section I08 of line I08 whichis within light spot X, then varies in the samemanner as the height oflight spot X, and in relation to the variation of the length w of levelI08. In the case of light spot'x, therefore, the area of portion A is nolonger'a function of the product of a variable and a constant, but it isa function of the product of' two variables. Furthermore, since the oneof these variables, namely, h, is a function of the other variable,namely, w, theiarea of portion A is, in the case of light spot X, anonlinear function of the area of portion A, it is, in the case of lightspot X, a non-linear function of w. It will thus be seen that, bydefining the height of light spot X so that it varies in an appropriatemanner, any desired non-linear relationship may be established betweenthe exposure of level 206 and the length of level I06. It is understoodthat the establishment of such a non-linear relationship in the opticalsystem of Figs. 1 and 2' will generally result in distortions of thevariable density sound track 38 produced on film P by printing. But thisresult is at times desirable, for example, to compensate for distor-'tions arising from other sources, as will be explained hereinafter.

A simple non-linear relationship between the exposure of level 206 andthe length of level I06 may be established, for example, by forming, inthe plane of film N the uniformly illuminated light spot I0 shown inFig. 7. Light spot I0 has a straight edge II which extends slantwise ina horizontal direction so as to be inclined with respect to verticaledges. 12 and I3 of light spot I0 and to point upward from edge 12 toedgel3. Horizontal edge 14, on the other hand, of light spot I0 is notonly straight but also perpendicular to vertical edges I2 and I3.

With this shape of light spot I0, the distance of its horizontal edge IIfrom its horizontal edge It varies in such a manner that it increasesfrom its vertical edge 12 to its vertical edge 13. Consequently, thelength h of the section I03.of vertical line I08 which is within lightspot 10, increases with the distance of point I0! from the vertical edgeI02 of sound track S, that is, with the increase of the length w oflevel I06. Since inclined edge II is straight, the increase of h is alinear function of the increase of w. In the case of light spot 10,therefore, the two factors 10 and h. to

whose product the area of portion A is related, are variable, and theyare interdependent in such a manner that his a linear function of 10.Hence,

the area of portionA is in this case a second degree function of w, andso is the exposure of is bounded by a straight and inclined edge whichpoints downward from vertical edge 12 to vertical edge 13, the area ofportion A is again a secand degree function of w. But it now decreaseswhen to increases so that the rate of change, of

the area of portion A new decreases when w increases.

In Fig. 8 there is shown another example of a uniformly illuminatedlight spot the formation of which in the plane of film N will establisha nonlinear relationship between the exposure of level 206 and thelength of level I06. Light spot 80 has a curved edge 8I whose curvatureis of a parabolic character. Curved edge 8I extends horizontally linearfunction or. w. Finally, since with any I shape of theuniformlyilluminated light spot in the plane of film N the exposure Of level 208is a from vertical edge'82 of light spot to vertical edge 33 thereof insuch a manner that its slope increases as it approaches edge 83.Horizontal edge 88, on the other hand, of light spot 80 is not onlystraight but also perpendicular to vertical edges "and 83.

With this shape of light spot 80, the distance of its horizontal edge 8|from its horizontal edge 84 again varies in such a manner thatitincreases from its vertical edge 82 to its vertical edge 83.Consequently, the length it of the section I03 of I82 and I84, of edges82 and 84 of light spot respectively, and light spots vertical line I88which is within light spot 88,

again increases with the distance of point I81 from the vertical edgeI82 of sound track S, that is, with the increase of the length w oflevel, I88. Since, however, curved edge '8I is a parabola, the increaseof it now is a second degree function of the increase of w. Inthe caseof light spot 88, therefore, the two factors w and h to whose productthe area of portion A is related, are interdependent in such a mannerthat h is a second de-- gree function of 10. Hence, the area of portionA is in this case a third degree function of w, and so is the exposureof level 288.

It should be noted that, since the slope of parabolic edge 8I increasesas it approaches vertical edge 88, It increases when w increases so thatthe rate of change of the area of portion A increases when w increases.When, therefore, light spot 88 is bounded by a'parabolic edge whoseslope decreases as it approaches vertical edge 83, the area of portion Ais again a third degree function of w. But It now decreases when wincreases so that the rate of change of the area of portion A nowdecreases when 10 increases. v

when the uniformly illuminated light spots I8 and 88 are shaped asillustrated in Figs. 7 and 8,

h increases with w over the entire horizontal extension, or width, ofthese light spots. But the uniformly illuminated light spot in the planeof film N, may also be shaped so that It increases with w over one partof its width, and decreases when w increases over another part of itswidth. A uniformly illuminated light spot of a shape resulting in afunctional relationship of this kind is light spot 18a shown in Fig. 'IAas bounded by Another example of this typev inclined edge I8. of lightspot is light spot 88a shown in Fig. 8A.

Light spot 88a is bounded by curved edge 88, and

the curvatureof edge 88 is of a parabolic character. When, therefore, inthe case of uniformly illuminated light spots 18a and 88a w increases,the rate of change of the area of portion A- inover another partthereof.

Throughout the foregoing 7, TIA, 8, and 8A, it has been assumed thatlight spots I8, 18a, 88, and 88a are so positioned in the plane of filmN that their vertical edges I2 and 82, respectively, are in alignmentwith straight boundary I82 of portion T, and their horizontal edges 14and 84 parallel'to horizontal edge I84 of sound respectively, thereforein accordance with. the increase'of w is concerned.

Light spots 18 and 18a (Figs. 7 and 7A) are horizontally bounded byperpendicular and straight edge 14 and'by inclined edges'II and 18, 88and88a (Figs. 8 and 8A) are horizontally bounded by perpendicular andstraight edge 84 and by curved edges 8I and '88, respectively. Sinceinclined edges'll and I8 arestraight throughout their entire lengths,the functional relationship between w and h is of a linear characterover the entire .width of light spots 18 and 180. 'Similarly, since thecurvature of edges 8I and 88 is parabolic throughout their entirelengths, the functional relationship description of Figs. 8

a and 18a, and of a third degree character over the creases over onepart of their width and decreases the exposure of film P. so as tocompensate for g between w and h is of a second degree character overtheentire widthof light spots 88 and 88s,,

The functional relationship, therefore, between, and the area of portionA is ofja secondidegr' character over the entire width, light spots 18,,

entire width of light spots 88 and 88a.

But, in. addition to being bounded by a p pendicularand straighthorizontal edge, the uni-, formly illuminated light spot X may also bebounded by a horizontal edge whose contour is in;

part inclined and straight and in part parabolic so that the functionalrelationship between a and h' is of a linear character over one part ofthe width of the light spot, and of a second de-' gree character overanother part of its width. Moreover, any other complex character may begiven to this functional relationship by appropriately defining thecontour, of one of the two horizontal edges, and hence of the height, ofthe uniformly illuminated light spot X. As will readily be understoodfrom the foregoing explanations, it is the character of the functionalrelationship between w and h which in any case determines the characterof the functional relationshipbetween w and the area of portion A, andhence the exposure of film P at level 288. The exposure of level 288,therefore, may be brought into any desired functional relationship to wby sodeflning the height of the uniformly illuminated light spot X thatit varies in a manner establishing the appropriate determiningfunctional relationship between w and h. This principle is applied in apresently preferred embodiment of the invention as follows: v I

As is well known in the art, the light transmission of a developed filmis not linearly related to its exposure. The variations inlighttransmission of the variable density sound track 88 after thepositive film P has been developed, thus are not linearly related to thevariations in amount of thelight flux from lamp filaments III which was,

in the optical system of Figs.- 1 and 2, transmitted to filmv P by thetransparent portion T of the variable area sound track S. If, forexample, the

amount of light flux transmitted by portion T was linearly related tothe width of portion T because the uniformly illuminated rectangularlight spot H was formed in the, plane of film N (Figs. 4 and 6), thelight transmission of the developed sound track 88 isnot linearlyrelatedto the width of portion '1. Hence, sound track 88 is in this case notdirectly usable for the reproduction of undistorted sound. If,therefore, it is desired to reproduce undistorted sound directly fromsound track 88, there must be established, in the optical system ofFigs. 1 and 2, a non-linear relationship between the width of portion Tand the non-linearity of the emulsion characteristic of film P. In thismanner, a linear relationship is established between the width ofportion '1 and the light transmission of sound track 88 afterdevelopment of film P, which condition allows for the reproduction ofundistorted sound directly from sound track 88.

It must nowbe remembered that, according to the present invention, anydesired relationship between the exposure of film P at horizontal level288 and the length 10 of the conjugate level I88 of portion T maybeestablished,'in the optical system of Figs. 1 and 2, byso. defining theheight of the uniformly illuminated light spot X that it varies in amanner establishing the appropriate determining functional relationshipbetween to and the length h of the section |09of the vertical line Iwhich is within the light spot. The compensating non-linear.relationship described in thepreceding paragraph, therefore, isestablished in the optical system of Figs. 1 and 2 by so definingthecontourof one of the two horizontal edges of a light spot embodying theuniformly illuminated light spot X, for example, of the horizontal edge9| of the light spot 90 shown in Fig. 9, that the height of light spot90 varies in the proper manner. Curved edge 9| extends horizontallybetween the vertical edges 92 and 99 of light spot 90, while thehorizontal edge 94 of light spot 90 is straight and perpendicular tovertical edges 92 and 99. The distance of horizontal edges 9| and 94from one another, that is, the height of light spot 90,-therefore variesin the manner indicated by'the contour of edge 9|. The disposition,finally, of light spot 90 with respect to sound track S is such that itsvertical edge 92 is in alignment with the straight boundary I02 ofportion T and its horizontal edge 94 parallel to horizontal edge I04 ofsound track 8.

The exact contour of curved edge 9| is determined by first determiningthat relationship between w and the exposure of level 206 which resultsin a linear relationship between w and the light transmission of level209 after film P has .general character represented by the curve Q inFig. 10.

Referring again to Fig. 9, curved edge 9| of light spot 90 isintersected. at point R by the ver-' 'tical line I00 through theendpoint I01 of level I09. The distance of point R from vertical edge 92is, on account of the geometrical relationships equal to the length w oflevel I09, while the distance of point R from horizontal edge N, thatis, the height of light spot 90, is equal to the length h of the sectionI09 of line I00 which is within light spot 90. Edge 9| now is curved sothat h is linearly related to the slope of curve Q at the point Uthereon whose abscissa is w. With this contour'of edge 9| there is thenestablished the desired determining relationship between w and h.Furthermore, according to a well known principle of mathematics, curve Qwill result when the area of the portion of light spot 90 betweenvertical edge 92 and vertical line I09, that is, the

area of portion A swept out by level I00 when it traverses light spot90, is plotted against the distance of point R from edgev 92. that is,the length w of level I00. The area of portion A, therefore, is in thecase of light spot 90 a nonlinear function of w, the non-linearity beingof the character represented by curve Q. Since the exposure of level 208is, in the optical system of Figs. 1 and 2, linearly related to the areaof portion A, curve Q also represents the character of the non-linearrelationship between 10 and the exposure of level 200 when the uniformlyilluminatedlight spot 90 is formed in the plane of film N. Thischaracter is, on account of the manner in which curve Q was derived,such that the light transmission of level 209 is a linear function of wafter film P has been developed; provided,

of course, that the above mentioned linear relationship between hand theslope of curve Q is such that, under the conditions of the actualprinting operation, the exposure of level 200 falls along curve Q andnotalong a curve parallel thereto.

It will thus be seen that, with the uniformly illuminated light spot 90formed in the plane of film N of the optical system of Figs. 1 and 2, alinear relationship is established between the width of the transparentportion T of the variable I area sound track S and the lighttransmission of the variable density, sound track 38 after the positivefilm P has been developed. As has been pointed out hereinabove, thisresult is desirable if undistorted sound is to be reproduced directlyfrom sound track 39. However, the present invention may also be used .toestablish any desired non-linear relationship between the width ofportion T and the light transmission of the developed sound track 20.Such a non-linear relationship is desirable, for example, if thedeveloped sound track 39 is to be printed from film onto a film F (notshown) by means of either the optical systemof Figs. 1 and 2 or aconventional sound printing optical system. In order to make possiblethe reproduction of sound from the variable density soundtrack thusproduced on film F without causingdistortion due to the non-linearity ofthe emulsion characteristics of film P and film F, the lighttransmission of the developed sound trackon film F must he a linear-function of the width of portion T. This condi- -.tion is satisfiedwhen a non-linear relationship is established between the width ofportion T and the light transmission of the developed sound track 38 soas to compensate for the non-linearity of the emulsion characteristicsof film P and film F. According to the present invention, a nonlinearrelationship or sucha character is estab lished again by appropriatelydefining, in the optical system of Figs. 1 and 2, the height of a shownin the drawings and described hereinabove,

light spot embodying the uniformly illuminated light spot X, and this isdone again by suitably defining the contour of one of the two horizontaledges of the light spot. The exact contour of this curved edge isdetermined by first determining experimentally the curve representingthat relationship between the width of portion T and the exposure offilm P which results in a nonlinear relationship between the width ofportion T and the light transmission of the developed sound track 90of-such a character that a linear relationship is established betweenthe width of portion T and the light transmission of the developed soundtrack' on film F. By means of this curve, the horizontal edge then iscurved so as to make w and h interdependent in such a manner that h ilinearly related to the slope of the curve at a point thereon whoseabscissa is w. As in the case of curved edge 9|, h is the distance of aa point on the curved edge from the straight horizontal edge of thelight sp0t, that is, the height -of the light spot, while w is thedistance of this about that the light transmission of the devel- 1 opedsound track 30 has such a non-linear relationship to the width ofportion T that the light transmission of the developed variable densitysound track on film F will be a linear function thereof. It isunderstood that, in order properly to achieve this end, the abovementioned linearrelationship between h and the slope oi the curve mustbe such that, under the conditions of the actual printing operation, theexposure of film P falls along the aforementioned curve and not along acurve parallel thereto.

According to the present invention, there can thus be established in theoptical system of Figs. 1 and 2 non-linear relationships between thewidth of the transparent portion T of the variable area sound track Sand the exposure of the positive film P, whose character is such thatlinear relationships are established between the width of portion T andthe light transmission of the developed variable density sound trackeoneither film P or film F. This result is achieved in both cases withoutimposing restrictions, on account of their emulsion characteristics, onthe choice of the film stocks which are usable as film P and film 1',respectively, and without necessitating a reduction of the volume rangeof the. reproduced sound by the mode of employment of those film stocks.1 I

Throughout the foregoing description of the present invention it hasbeen assumed that the variablearea sound track 8 on film N is of theunilateral type asillustrated in Flgsc4, 6 and 9. However, as hasbeenpointed out in application Serial No. 449,798, the variable area soundtrack on film N which is to be converted into the variable density soundtrack on film P by means of the printing optical system of Figs. 1 and2, may also be of the bilateral, or symmetrical, type, and in this case,too, there may be employed the invention disclosed and claimed in thisspecification. The symmetrical variable area sound track on film N may,for example, be an original negative which has its transparent portiondivided by its opaque portion 01 into two portions T' and T as has soundtrack 81 shown in Fig. 11A. As'

likewise shown in Fig. 11A, sound track 81 is symmetrical about itsvertical center line C1-C1.

Consequently, any light spot formedin the plane of film N as anembodiment of the unformly illuminated light spot 1: must'be symmetricalabout its vertical center line as is light spot I shownin Fig. *llA asan example of such a light 'and I01", respectively, on the undulatingboundaries between portion 01 and portions T and T",

' respectively, and broken vertical lines I00 and I00" are drawn throughpoints I01 and I01",

respectively. It has been explained hereinbefore that, when employedwith sound track S1, any light spot formed in the plane of film N as anembodiment of the uniformly illuminated light spot I is symmetricalabout its vertical center line and, furthermore, that this center lineis in alignment with the center line C1-C1 of sound track 81. For thatreason, and because sections I00 and I00" are symmetrically disposedwith respect to center line C1--C1, h is the length of both the sectionsI09 and I00" of vertical lines I00 and I00" within'any such light spot.There are swept out, therefore, by the transparent level consisting ofthe two sections I00 and I06" the two portions A and A" of the lightspot embodywhich extends horizontally so as to be inclined with respectto vertical edges I12 and Ill of light spot I10. The apex of edge III ison center line I10-I10 of light spot I10, and the straight legs of edge"I both point upward from edges I12 line. Moreover, the vertical centerline of the light spot embodying the uniformly illuminated light spot xmust be in alignment with the cenand I13. Horizontal edge I14, on theother hand, of light spot I10 is not only straight but alsoperpendicular to vertical edges I12 and I10. spot I10 is symmetricalabout its center line I10-I10 so that the distance of horizontal edge Ifrom horizontal edge I14 decreases on both 1 sides thereof, and centerline I10-I10 is in alignment with center line C1-C1 of sound track 81.

. Referring now to the explanations given hereinabove in connection withFig. 7, it will readily be understood that with light spot I10 boundedby edge Hi the total area of portion A and A" swept out by thetransparent level consisting of sections I00 and I00", and hence theexposure of film P at level 200, is a second degree function of thetotal length w of that level. Furthermore, since the straight legs ofV-shaped edge I1I both point upward from vertical edges I12 and I13, h

increases when w increases so that the rate of changeof the exposure oflevel 200 increases with the increase of w. When, therefore, light spotI10 I is bounded by a. V-shaped edge whose straight less ter line-C1C1of sound track 51 asis the vertical centerline I10-I10 of light spotI10.

On account of the division into the two portions T and T" or thetransparent portion of sound track 81 by its opaque portion 01, thetransparent both point downward from vertical edges I12 and I13, thetotal area of portions A and A" swept out by the transparent levelconsisting of secdore, 'is obtained with light spot I10 when symmetricaltrack Sris on film, N, as with light spot 10 when unilateral track S ison film N.

It should be noted that, in the same manner as it is conjugate to thelevel I00 on portion T of unilateral sound track S, level 200 on film Pisf I in the optical system of Figs. 1 and 2, conjugate to the levelconsisting of sections I00 and I00" on portions '1" and'l" ofsymmetrical sound track S1. Furthermore, although this level is dividedinto two sections, the conjugate level 200 on film P is undivided forthe reasons set forth in application Serial No. 449,798.

Another type of symmetrical variable area sound track is sound track 8:shown in Fig. 113. Sound track S2, which may have been obtained byprinting from a sound track such as sound track S1 or directly recordedby means of the reversal method, has its opaque portion divided by itstransparent portion T2 into two portions and 0'. As shown in Fig. 113,sound track S2 is symmetrical about its vertical center line C2C2. Aswith sound track S1, therefore, any light spot employed with sound trackS: as an embodiment of the uniformly illuminated light spot X, must besymmetrical about its vertical center line as is 11B. Level I06 issymmetrical about center line C2-C2 with its endpoints mm and M1!) onthe Furthermore, since the straight legs of V-shaped edge 2" both pointdownward from vertical edges 212 and 213, h increases when w increasesso that the rate of change of the exposure of level 208 increases withthe increase of 10. When,

therefore, light spot 210 is bounded by -a V- shaped edge whose straightlegs both point upward from vertical edges 212 and 213, the area ofportion A swept out by the undivided level I08 of portion T2 is again asecond degree function of the length w of that level. But 21. nowdecreases when to increases so that the rate of change of the exposureof level 206 decreases undulating boundaries between portion T2 andvtherefore, of the light spot embodying the uni-' formly illuminatedlight spot .X is swept out by the undivided level I06, and portion A issymmetrical about the vertical center line of this light spot. The areaof portion A thus is again a function of the product w x h. and anon-linear function of w, w being the length of level I06 "and h thelength of the sections Illa and I081: of vertical lines I08a and I08bwhich are within the light Y spot embodying light spot X. Sections M811and I08b are of equal length because level I06 is symmetrical aboutcenter line C2C:, the light spot embodying light spot X is symmetricalabout its own-center line, and the two centerlines are in alignment withone another.

For example, in order to make the area of portion A a second degreefunction of w, the uniformly illuminated light spot 210, shown in Fig.113, is formed in the plane of .illm N. Light spot 210 has a v-shapededge 2 which extends horizontally so as to be inclined with remect tovertical edges 212 and 213 of light spot 210. The apex of edge 2" is oncenter line 215-215 of light spot 210, and the straight legs of edge 21Iboth point downward from edges 212 and 213. Horizontal edge 214,'on theother hand, of light spot 210 is not only straight but alsoperpendicular to vertical edges 212 and 213. Light spot 210 issymmetrical about its center line 21521l 'so' that .the distance ofhorizontal edge 2" from horizontal edge 214 increases on'both sidesthere-.

by edge 2' the area of portion A swept out by the undivided level I08 ofportion Ta, and hence the exposure of film P at level 208, is a seconddegree function of the length to of that level.

with the increase of w. The same result, therefore, is obtained withlight spot 210 when symmetrical track S2 is on film N, as with lightspot I10 when symmetrical track S1 is on film N. As a matter of fact,when light spot I10 is bounded by a V-shaped edge whose legs both pointdownward from vertical edges I12 and I13, it is identical with lightspot 210 and, conversely, when light spot 210is bounded by a V-shapededge whose legs both point upward from vertical edges 2 12 and 213, itis identical with light spot I10.

Uniformly. illuminated light spots I10 and 210 thus are adaptations oflight spot 10 for use with the symmetrical variable area sound tracks S1and S2, respectively. In like manner, the uniformly illuminated lightspots I80, HM, and I80a, shown in Figs. 12, 13, and 14, respectively,are adaptations for 'the same purpose of light spots 80, 10a, and 80a,respectively. For example, light spot I80 may be bounded horizontally bystraight edge I84 and curved edge I8I whose curvature is of aparaboliccharacter and whose distance from horizontal edge I84 decreases on bothsides of the center line I85I85 of light spot I80.

The employment, therefore, of light spot I80 in conjunction with eithertrack S1 or track Sz results in the exposure of level 206 being a thirddegree function of 10. But the rate of change of the exposure increaseswith w when. light spot I80 is employed with track S1, while itdecreases with the increase of w when light spot I80 is employed withtrack S2. apply in the case of light spot I10a which is bounded byinclined edge I18, and of light spot I80a which is bounded by parabolicedge I88. In accordance with the explanations made hereinabove, lightspots I80, H00, and I80a, are symmetrical about their vertical centerlines are in alignment with the center lines C1C1' and C2C2 of tracksS1-and S2, respectively, in

the manner illustrated in Figs. 11A and 1113 for the vertical centerlines I15I 15 and 215-215 of light spots I10 and 210, respectively.

Finally, the uniformly illuminated light spots I and 290 tively, areadaptations of light spot 80 for use with the symmetrical variable areasound tracks S1 and S2, respectively. Light spot I80, which is to beused in conjunction with track S1, is bounded by the curved edge I!"which extends horizontally between the vertical edges I82 and I of lightspot I90, while the horizontal edge I of light spot I80 is straight andperpendicular to vertical edges I82 and I93. The distance of horizontaledges I8I and I94 from one an- .other, that is, the height of light spotI90, there- Light spot m is symmetrical about its vertical Similarconsiderations shown in Figs. 15A and 15B, respec- I center lineI95,-I95 and, when light spot I90 is formed in the plane of film N,center line I95'I99 is in alignment with center line 01-01 of track S1,while vertical edges I92 and I93 are in alignment with the straightboundaries I02 and I02 of portions T' and T",

respectively. Furthermore, edge I9I is intersected at the points R. andR" by the vertical lines I90 and I08" through the endpoints I01" andI01" of sections I06 and I09", respectively.

'been pointed out hereinabove-while the distance of points R and R" fromhorizontal edge I94, that is, the height of light spot I90, is equal tothe length h of the sections I09 and I09" of lines I09 and I08,respectively, which are within light spot I90; compare Figs. A and 11A.

The exact contour of curved edge I9I is deter-- mined essentially in themanner described hereinabove in connection with Figs. 9 and 10 for thecurved edge 9I of light spot 90. That is to say, aftercurve Q hasbeen'determined by experiment, horizontal edge I! is curved so that h islinearly related to the slope of curve Q at the point U thereon when wand 10'', respectively, are equal to half the abscissa of point U.Curved edge I9I then is so disposed with respect to center line I9l--I9lthat the length thereof is equal to the value of h for the maximum valueof the total length w of the transparent level consisting of sectionsI00 and I00", that is, of the width of portions T and T".

Light spot 290 which is to be used in coniunction with track $2, on theother hand, is bounded by the curved edge 29I which extends horizontallybetween the vertical edges 292 and 299 of light spot 290, while thehorizontal edge 294 of light spot 290 is straight and perpendicular tovertical edges 292 and 203. The distance of horizontal edges 29I and 294from oneanother, that is, the height of light spot 290, therefore variesin the manner indicated by the contour of edge 29I,

Light spot 290 is symmetrical about its vertical center. line 290-295and, when light spot 290 is formed in the plane of film N, center line290-290 is inalignment with center line C2-C2 of track 82, whilevertical edges 292 and 299 are in alignment with the straight boundariesI02a and I02b of portions 0' and 0", respectively. Furthermore, curvededge 29I is intersected at the point Ru and Rb by the vertical linesI00a and I0lb through the endpoints WM and I0'Ib, respectively, of levelI06. On account of the geometrical relapoint U. Curved edge 29I then isso disposed with respect to center-line 299-495 that the length thereofis equal to the value of h for the zero value of the length 111 of levelI06, that is, of the width of portion Ta. 1

Thus, when the uniformly illuminated light spot I90 is employed inconjunction with the symmetrical variable area sound track S1, and theuniformly illuminated light spot 290 inconJunction with the symmetricalvariable area sound track S2, there is established a non-linearrelationship between w and the exposure of level 209 whose character issuch that the light transmission of level 200 is a linear function of wafter film P has been developed; provided, of course, that the abovementioned linear relationship between h metrical about their respectivevertical center lines, and which are bounded horizontally by curvededges of appropriate contours, the light transmission of level 209 mayalso be made a nonlinear function-of 10 after film P has been developed.The non-linear relationship between the width of portions T and T", orportion T2, and the light transmission of the developed variable densitysound. track 90 may, for example, be of such a character that, whensound track 3915 printed from film P onto a film F (not shown), thelight transmission of the variable density sound track thus produced onfilm F is, after development of film F, linearly related to the width ofportions T and T", or portion T2. In order actually to establish anon-linear relationship of this character, one of the two horizontaledges of the uniformly illuminated ,light spots may be curvedessentially in the manner explained hereinabo've with reference to theestablishment of a 0 relationship of the same character in case thatunilateral sound track 8 is on film N. First, there is determinedexperimentally the curve representtionships involved in this case, thedistance w/2 of points Ba and Rb from center line 295-490 is equal tohalf the length w of level I00, while their distance from horizontaledge 294, that is, the height of light spot 290, is equal to the lengthh of the sections I090 and I09b of lines I0 and 091), respectively,which are within light spot 290; compare Figs. 15B and 11B.

The exact-contour of curved edge 29I is determined essentiallyin themanner described hereinabove in connection with Figs. 9 and 10 forcurved edge 9| of light spot 90. That is to say. after curve Q has beendetermined by experiment, horizontal edge 29I is curved so that h islinearly related to the slope of curve Q at the point U thereon when w/2is equal to half the abscissa of the one of these two points from theone vertical edge of the light spot, and the distance of the other pointfrom the other vertical edge of the light spot, are in the case of thelight spot which is to be used in conjunction with track S1 both equalto halt the abscissa oi the point on the curve. The curved horizontaledge, therefore, is in this case so disposed with respect to thevertical center line of the light spot that the length thereof is equalto the value of h for the maximum value of the width of portions T" andT".

In the case of the light spot which is to be used in conjunction withtrack S2, on the other hand, the distance of the two points'on thecurved edge from the vertical center line of the light spot is madeequal to half the abscissa of the point on the curve.. This curvedhorizontal edge, therefore, is so disposed with respect to the vertical2,901,979 center line of the light spot that the length thereof is equalto the value of h for thezero value of the width of portion T2.

Since the two last mentioned light spots are, in general, similar tolight spots I99 and 299, reference is made to FlgsnlA'and 153 by way offurther explanation. Furthermore, it is understood that, when thesetwolight spots are formed in the plane of film N, their vertical centerlines are in alignment with center lines C1C1 and C2-C1 of tracks S1 andSe, respectively, and that, in order properly to establish thenon-linear relationship characterized in the last but precedingparagraph, the above mentioned linear relationship between hand theslope of the curve must be such that, under the conditions of the actualprinting operation, the exposure of film P falls along theaforementioned curve and not along a curve parallel thereto.

Horizontal edges 14, 84, 94, I14, 214, I94, I94,

and 294', are shown in Figs. 7 to 9 and 11A to 15B,

and have been described hereinabove, as being straight and perpendicularto the two vertical edges of light spots 19 and 19a, 99 and 89a, 99, I19and "9:1, 219, I99 and I89a, I99, and 299. respectively. Any. desireddetermining relationship between and it, however, may also beestablished by defining the shape of the uniforml illuminated light spotX sothat neither of its two horizontal edges is straight and/orperpendicular to its two vertical edges. The only requirementsthat mustbe fulfilled in any such case are that the distance from one another ofthe horizontal edges, that is, the height, of the light spot varies andthat, when employed with symmetrical variable area sound tracks such assound tracks S1 and S2, the light spot is symmetrical about its verticalcenter line. Furthermore, the law governing the variation of the heightof this light spot must result in the desired functional relationshipbetween w and h.

The uniformly illuminated light spot 919 shown in Fig. 16, for example,which is bounded by the two inclined horizontal edges 8H and 914, mayreadily be substituted for light spot 19 when the .latter' light spot isbounded by inclined edge 1| and perpendicular edge 14.

Light spots 19, 19a, 99, 89a, 99, I19, 219, I1Ila, I99; I99a, I99, 299,and 919, have been shown in Figs. 7 to 9 and 11A to 16 and describedhereinabove by way of example asembodiments of the uniformly illuminatedlight spot X whose shape is defined so that it has two horizontal edgesand that its height, that is, the distance of its horizontal edges fromone another, varies.

pending upon the ratio of imagery given to spherical lens l3.

There'is another way of forming the uniformly illuminated light spot Xin the plane of film N of the optical system of Figs. 1 and 2. Thiswayconsists in retaining the rectangular opening I9,

- or anyother suitable opening, in screen I9 and providing adjacent tothe plane of film N an additional screen I9 with an opening whoseoutline corresponds to the shape of a light spot embodying light spot X,for example opening I9, as shown in Fig. 18. The resulting arrangementis illus- I trated in Fig. 19 which is asection along the axis of theoptical system of Figs. 1 and 2 showing the parts thereof from lampfilament I0 up to, and including, film N. It should be noted that screenl9 may be placed on either side of the plane of film N, that is, betweenthis plane and either spherical lens I9 as shownin the drawings, orcylindrical lens 99. The dimensions of the opening in screen I9 areapproximately those which it is desired to give to the light spot to beformed in the plane of film N, and care must be taken that the openingin screen I9 is fully covered by the image of the opening in screen I5formed in the plane of film N by spherical lens l9, as indicated in Fig.18 by the broken line I16.

In the above explanations, the present invention has been described byway of example. as applied to the optical system of Figs. 1 and 2 whichare identical with Figs. 1 and 2 of application Serial No. 449,798.However, the present invention may likewise be applied to the otheroptical systems disclosed in that application. For

. example, screen I! may be provided with open- In the optical system ofFigs; 1 and 2, the shape of the uniformly illuminated light spot inv the.plane of film N may be defined so that it is an embodiment of lightspot X by providing in screen I9 not the rectangular opening I8 but "anopening whose outline corresponds to the shape of a particularembodiment of light spot X. If,

forexample, it'is desired to form in the plane illuminated light spot offilm N the uniformly "bounded by inclined edge. 1I (Fig. 7), there isprovided in screen I5 the opening I9, shown in Fig. 17, whose outlinecorresponds to this shape of light spot 19. The dimensionsof opening I9have been shown in Fig. 17. by way of example as being those of lightspot 19 as shown in Fig.

7. However, the dimensions of opening I9 may also be larger or smallerthanthe dimensions of light spot 19, their size in a given actualembodiment of the optical system of Figs. 1 and- 2 deing I8, or anyother opening whose outline corresponds to the shape of a light spotembodying light spot X, also in the optical system of Figs. 6 and 7 ofapplication Serial No. 449,798. Al-

ternatively, additional screen I9 may'be placed adjacent to the plane offilm N of this optical system in the manner explained hereinabove inconnection with Figs. 18 and 19.

The present invention may furthermore be applied to the optical systemof Figs, 8 and 9 of application Serial No. 449,798 when it is employedwith screen I9 placed adjacent to the plane of film N and screen 99placed in front of the-plane of film P, as disclosed in the descriptionof that application. In this case, screen Il may be provided, in placeof rectangular opening I9, with an opening of such an outline as torestrict to the shape of the desired embodiment of light spot X theuniformly illuminated light spot which, in the optical system of Figs. 8and 9 of application Serial No. 449,798, is formed in the plane offilm Nby the action of spherical condenser I2. In the same manner, the presentinvention may be applied when the arrangement for forming a uniformlyilluminated light spot in the plane of film N shown in Figs. 8 and 9 ofapplication Serial No. 449,798 is employed with the optical system ofFigs. 6 and 7 of that application as disclosed in thedescriptionthereof. 1

Moreover, the application of the present invention is not limited to theoptical systems of application Serial No.v449,798, but. the presentinvention may also be applied in substantially the same manner, and tothe same advantages,, to the optical systems disclosed and claimed inl?atent No. 2,366,040. Considering first the opticalfsystem's shown inFigs. 4 and 5, Figs. 7 and}? and Figs. 9 and 10, of Patent No. 2,36,04Q,the,present invention may be appliedtherto in thd'seime disclosed in thedescription of Patent No.

2,366,040, screen l may be placedadjacent to the plane of film N andscreen 35 in front of the plane of him .P in the modification of theoptical system at Figs '7 and. 8 of that application which is shownin,Figs.- l3 and 14 thereof. In this case, the present ,Linverltionmaybe applied by providing in screen ii, in place of rectangular openingIS, an opening of such an outline as to restrict to the shape of thedesired embodiment of light spot X the uniformly illuminated light spotwhich, in the. opticalsystem of Figs. 13 and 14 of Patent No, 2,356,040,is formed in the plane of film N by the actionof spherical condenser II.In the same ,inanner, the -,.present invention may be applied when thearrangement for forming a uniformly illuminated light spot in the planeof film N shown in ,Figs. 13'and 14 of Patent No. 2,366,040 is ployedwith the optical systems .of Figs. 4 and 5 andFigs. 9 and, 10 of thatapplication as disclosed in the description thereof In. themodification'of the optical system of Figs. 4 and 5 of Patent No.2,366,040 whichis shown in Figs. 11- and 12 thereof,screen ilis placedadjacentto the field lens. In this case, too, the present invention maybe applied by providing in screen II, in place of rectangular openingIS, an opening of such an outline as to restrict to the shape of thedesired embodiment of light v spot X the image-formed, in the opticalsystem 'of Figs. 11 and 12 of Patent No. 2,366,040, at point A byobjective 20 oi the uniformly illuminated light spot which, in itsturn,-.- is formed in the plane of. film N of this optical "system bythe action of spherical condenser l2. Since the image formed atsaidpoint A is an enlarged one, the

opening in screen l5 can be made inthis case on an enlarged scale andtherefore more accurately, which is particularly advantageous when itsoutline is of a complicated,character, for example, when the outline isto correspond to the shape oflight spots 90 (Fig. 9) or I00 (Fig. 15A.)

The same advantage may be enjoyed by placing v, additional screen iswith an opening whose outline corresponds to the shape of a light spotembodying light spot X, adjacent to the fieldlens in first mentionedcase, the opening whose outline corresponds to the shape of light spot Xmay be either in screen l5, screen i5 being placed either adjacent tothe plane of film N or at a position where the opening therein may beimaged in the plane of film N by the action of spherical lens l3, or itmay be in additional screen is which is placed adjacent to the plane offilm N. In the second mentioned case, the openin may be either in screenIt or in screen is, either screen being placed adjacent to the fieldlens and objective 20 being in both cases the means acting in both thevertical and horizontal planes referred to above.

When placed adjacent to the plane of film N or the field lens, screen l5and screen l9 may be placed on either side of the plane of film Northefield lens as has been pointed out hereinabove in connection with thepositioning of screen lain the optical system of Figs. 1 and 2.

The opening in screen I5, or in additional screen ID, has been describedhereinabove as an opening whose outline corresponds to the shape of aparticular embodiment of the uniformly illuminated light spot X. Asillustrated by the relationship between opening l8 (Figs. 17 and 18) andlight spot I0 (Fig; 7), this description means that, in general, thisopening has two horizontal edges whose distance from one another, thatis, the height of the opening, varies and that, in particular, itsheight varies in the manner characteristic for the embodiment of lightspot X to whose shape its outline corresponds. Furthermore, in case thatits outline corresponds to the shape of an embodiment of light spot Xfor use with a symmetrical variable area sound track such as soundtracks Si and S2 (Figs. 11A and,

11B) the opening has a vertical center line about which it issymmetrical so that its height varies in the same sense on both sides ofits center line.

The opening then defines the uniformly illuminated light spot embodyinglight spot X in such a manner that it has a vertical center line whichis in alignment with the vertical center line of the symmetricalvariable area sound track when film N moves vertically through itsplane. This condition must be satisfied when the light spot the opticalsystem of Figs. 4 and 5 of Patent No.

It should be noted that it is immaterial for the application of, thepresent invention to the optical systems of Patent No. 2,366,040 whetherthe field lens employed therein is spherical as is lens 25 shown inFigs. 4 and 5 and '7 to 12 of thatapplication, or cylindrical with itscylinder axis vertical, as is cylindrical lens 45 shown in Figs. 13 and14 thereof. i

It will thus be seen that, in the optical systems disclosed and claimedin application Serial No.

embodying the uniformly illuminated light spot X is formed in the planeof him N-as illustrated, by way of example, in Figs. 11A and 11B andalso when, in the cases referred to in the preceding paragraph, itisformed at a position where a uniformly illuminated light spot formed inthe plane of film N is imaged by means acting in both the vertical andhorizontal planes.

In the foregoing description of the present invention, and in theappended claims, the term straightf'v in contradistinction to the termcurved, is used with reference to the edge of a light spot, or' anopening, as meaning that the contour of either the entire edge, or ofevery one of its parts, is a first degree curve. Straight edges withinthe meaning of the term as used throughout this specification thereforeare, for example, edge 18 of light spot (Fig. 7A) and edge ill of lightspot I10 (Fig. 11A) as well as edge I I of light spot 10 (Fig. 'l)

What is claimed is:

1. In a printing optical system wherein a uniformly illuminated lightspot is more or less obsoured when a negative film having thereon a variable area sound track whose transparentportion varies in width, movesvertically through a first plane; and wherein light flux emanating fromvarying in linear relation to the slope of a curve representing arelationship between said said uniformly illuminated light spot is, inthe vertical plane, focused at a position and, in the horizontal plane,diifusedat said position, whereby a light spot of vertically. varyingillumination is formed at said position; and wherein light fluxemanating from said light spot of vertically varying illuminationeffects the exposure of a posit ve film' when said positive film movesvertically through a second plane, whereby a variable densitysound trackhavin a lighttransmission is produced on said positive film; theprovision of means defining the height of said uniformly illuminatedlight spot: said defining means including a screen with an openinghaving a height,

' formly illuminated light spot is more or lessobscured when a negativefilm having thereon a variable area sound track whose transparentportion varies in width, moves vertically through -a first plane; andwherein light fiux emanating from said uniformly illuminated light. spotis, in the vertical plane, focused at a position and, in

' the horizontal plane, diffused at said position,

whereby a light spot of vertically varying illumination is formed atsaid position; and wherein light fiux emanating from said light, spot ofvertically varying illumination effects the exposure of a positive filmwhen said positive film moves vertically through a second'plane, wherebya variable density sound track having a light transmission is producedon said positive film; the provision of means defining the height ofsaid uniformly illuminated light spot: said defining means including ascreen with an opening having two horizontal edges, said horizontaledges being at adistance-from one another, and at least one of saidhorizontal edges being curved in such a manner that said distance variesin linear relation to the slope of the curve representing thatrelationship between said width of said transparent portion and saidexposure of said positive film which results in a substantially linearrelationship between said width and said light transmission of saidvariable density sound track after said positive film has beendeveloped. 4 3. In a printing optical system wherein a uniformlyilluminated light spot is more or less obscured when a negative filmhaving thereon a variable area sound track whose transparent portionvaries in width, moves vertically through a first plane; and whereinlight flux emanat ng from said uniformly illuminated light spot is, inthe vertical plane, focused at a position and, in the horizontal plane,diffused at said position, whereby a light spot of vertically varying.illumination is formed at said position; and wherein light fluxemanating from said light spot of ver- I tically varying illuminationeffects the exposure of a positive film when said positive film movesvertically through a second plane, whereby a variable density'soundtrackhaving a light transmission is produced on said positive film; theprovision of means defining the height of said uniformly illuminatedlight spot: said defining means including a screen with an openinghaving a height, and said height of said opening width of saidtransparent portion and said exposure of said positive film whichresults in a non-linear relationship between said width and said lighttransmission of said variable density sound track after said positivefilm has been developed, said non-linear relationship being such that,when a print is made of said variable density sound track, the lighttransmission of said print after development thereof is substantiallylinearly related to said width.

4; In a printing optical system wherein a uniformly illuminated lightspot is more or less obscured when a negative fihn having thereon avariable area sound track whose transparent portion varies in width,moves vertically through a first plane; and wherein light fiux emanatingfrom said uniformly illuminated light spot is, in the vertical plane,focused at a position and, in the horizontal plane, diffused at saidposition, whereby a light spot of vertically varying illumination isformed at said position; andwherein light flux emanating from said lightspot of vertically varying illumination effects the exposure of apositive film when said positive mm moves vertically through a secondplane, whereby a variable density sound track having a lighttransmission is produceiti on said positive film; the 'provision ofmeans definingthe height of said uniformly illuminated light spot: saiddefining means including a screen with an opening having two Y the slopeof a curve representing a relationship print after development thereofis substantially linearly related to said width.

5. In a printing optical system wherein a uniformly illuminated lightspot is more or less obscured whena negative film having thereon a.

variable area sound track whose transparent portion varies in width,moves vertically through a first plane; and wherein light flux emanatingfrom said uniformly illuminated light spot is, in the vertical plane,focused at a position and, in the horizontal plane, diflused at saidposition, whereby a light spot of vertically varying illumination isformed at said position; and wherein light flux emanating from saidlightspot of vertically varying illumination effects the exposure of apositive film when said positive film moves vertically through a secondplane, whereby a variable density sound track having a lighttransmission is produced on said positive film; the provision of meansdefining the height of said uniformly illuminated light spot; saiddefining means including a screen with an opening having a height, andsaid height of said opening varying in linear relation to the slope of acurve representing a relationship between said width of said transparentportion and said exposure of said positivefilm which results in anon-linear relationship between said width and said light transmissionof said variable density sound track after said positive film has beendeveloped.

. scured when a negative film having thereon a variable area sound trackwhose transparent portion varies in width, moves vertically through afirst plane; and wherein light flux emanating from said uniformlyilluminated light spot is. in the vertical plane, focused at a positionand, in the horizontal plane, diffused at said position, whereby a lightspot of vertically varying illumination is formed at said position; andwherein light flux emanating from said light spot of vertically varyingillumination effects the exposure of a positive film when said positivefilm moves vertically through a second plane, whereby a veriable densitysound track is produced on said positive film; the provision of. meansdefining the height of said uniformly illuminated light spot: saiddefining means including a screen with an opening having a height, andsaid height of said opening varyingin linear relation to theslope of acurve representing a non-linear relationship between said width of saidtransparent portion and said exposure of saidpositive film.

- 7. In a printing optical system wherein a uniformly illuminated lightspot is more or less obscured when a negative film moves verticallythrough a first plane, said negative film having thereon a variable areasound track which is symmetrical about its vertical center line, andwhose transparent portion varies in width; and wherein light flux.emanating from said uniformly illuminated light spot is, in the verticalplane, focused position; and wherein lightfiux emanating from said lightspot of vertically varying illumination effects the exposure of apositive film when said positive film moves verticallythrough a secondplane, whereby a variable density sound. track having a lighttransmission is produced. on said positive film; the provision of meansdefining the height of said uniformly illuminated light spot: saiddefining means including a screen with an opening having a verticalcenter line and two horizontal edges, said horizontal edges being at adistance from one another, and at least one of said horizontal edgesbeing curved in such a manner that said distance varies in linearrelation to the slope ofthe curve representing that relationship betweensaid width of said transparent portion and said exposure of saidpositive film whichfresults in a substantially linear relationshipbetween said width and said light transmission of said variable densitysound track after said positive film has been developed; said horizontaledges being so disposed with respect to said last mentioned center linethat said last mention effects the exposure of a positive film when saidpositive film moves vertically through a second plane, whereby avariable density sound track having alight transmission is produced onsaid positive film; the provision ofmeans definin the height of saiduniformly illuminated light spot: said defining means including a creenwith an opening having a vertical center line and a height, and saidheight of said opening varying in the same sense on both sides of saidlast mentioned center line and in linear relation to the slope of thecurve representing that relationship between said width of saidtransparent portion and said exposure of said positive film whichresults in a substantially linear relationship between said width andsaid light transmission of said variable density sound track after said'positive film has been developed; said opening being symmetncalaboutsaid last mentioned center line and defining said uniformly illuminatedlight spot in such a manner that said uniformly illuminated light spothas a vertical center line which is in alignment with said firstmentioned center line when said negative film moves through said firstplane. I

8 In a printing optical system wherein a uniformly illuminated lightspot is more or less obscured when a negative film moves verticallythrough a first plane,- said negative film having thereon a variablearea sound track which is symmetrical about its vertical center line.and whose transparent portion is divided in two by its opaque portionand varies in width; and

.wherein light flux emanating from said uniformvertically varyingillumination is formed at-said tioned center line is equal to saiddistance for the maximum value of said width, and said opening beingsymmetrical about said last mentioned center line and defining saiduniformly illuminated light spot in such a manner that said uniformlyilluminated light spot has a vertical center line which is in alignmentwith said first mentioned center'line when said negative film movesthrough said first plane.

9. In a printing optical system wherein a uniformly illuminated lightspot is more or less obscured when a negative film moves verticallythrough a first plane, said negative film having thereon a variable areasound track which is symmetrical about its vertical center line, andwhose undivided transparent portion varies in width; and wherein lightflux emanating from said uniformly illuminated light spot is, in thevertical plane, focused at a position and, in the horizontal plane,diffused at said position, whereby a light spot of vertically varyingillumination is formed at said position; and wherein light fiuxemanating from said light spot of vertically varying illuminationeffects the exposure of a positive film when said positiv film movesvertically through a second plane, whereby a variable density soundtrack having a light transmission is produced on said positive film; theprovision of means defining the height of said uniformly illuminatedlight spot; said defining means including a screen with an openinghaving a vertical center line and two horizontal edges, said horizontaledges being at a distance from one another, and at least one of saidhorizontal edges being curved in such a manner that said distance variesin linear relation to the slope of the curve representing thatrelationship between said width of said transparent portion and saidexposure of said positiv film which results in a substantially linearrelationship between said width and said light transmission of saidvariable density sound track after said positive film has beendeveloped; said horizontal edges being so disposed with respect to saidlast'mentioned center line that said last mentioned center line is equalto said distance for th zero value ofsaid width, and said opening beingsymmetrical about said last mentioned center line and defining saiduniformly illuminated light spot in such a manner that said uniformlyilluminated light spot has a vertical center line which is in alignmentwith said first mentioned. center line when said negative film movesthrough said first plane.

10. In a printing optical system wherein a uniformly illuminated lightspot is more or less obscured when a negative film moves verticallythrough. a first plane, said negative film having thereon a variablearea sound track which is symmetrical about its \vertical center line,and whose transparent portion varies in width; and wherein lightfiuxemanating from said uniformly illuminated light spot is, in'thevertical plane,

I focused at a position and, injthe horizontal plane,

diffused at said position, whereby a light spot of vertically varyingillumination is formed at said position; and 'wherein' light fluxemanating from said light spot of vertically varying illuminationeffects the exposure of a positivefilrn when said positive film movesvertically through a second plane, whereby a variable density soundtrack having a light transmission is produced on said positive film; theprovision of means defining the height of said uniformly illuminatedlight spot; said defining means including a screen with an openinghaving a vertical center line and a height,

and said height of said opening varying in the same sense on both sidesof said last mentioned center line and in linear relation to the slopeof a curve representing a relationship between said non-linearrelationship between said width and said light transmission of saidvariable density sound track after said positive film has beendeveloped, said non-linear relationship being such 1 that, when a printis made of said variable density sound track; the light transmission ofsaid print after development'thereof, is substantially linearly relatedto said width; said opening being I through a first plane, saidnegativefihn having thereon a .variable area sound track which issymmetrical about its vertical center line, and whose transparentportion-is dividedln two by its opaque portion and varies in width; andwherein light flux emanating from said uniformly illuminated light spotis, in the vertical plane, fo-

cused at a position and, in the horizontal plane, diffused at saidposition, whereby a light spot of vertically varying illumination isformed at said position; and wherein light fiui': emanating from saidlight spot of vertically varying illumination effects the exposure of apositive film when said positive film moves vertically through a secondplane, whereby a variable density' sound track having a lighttransmission is produced on said positive film; the provision ofmeans'defining the height of said uniformly illuminated light spot: saiddefining means including .a screen with an opening having a verticalcenter line and two sults in a non-linear relationship between saidwidth and said light transmission of said variable density sound trackafter said positive film has i been developed, said non-linearrelationship being such that, when a print is made of said variabledensity sound track, the light transmission of said print afterdevelopment thereof is substantially linearly related to said width;said horizontal edges being so disposed with respect to said lastmentioned center line that said last mentioned center line is equal tosaid distance for the maximum value of said width, and said openingbeing symmetrical about said last mentioned center line and definingsaid uniformly illuminated light spot in such am-anner that saiduniformly illuminated light spot has a vertical center line which is inalignment with said first'mentioned center line when said negative filmmoves through said first plane.

12. In a printing optical system wherein a uniformly illuminated lightspot is more or less width of said transparent portion and said ex-Dosure' of said positive film which results in a obscured when anegative film moves vertically through a first plane, said negative filmhaving thereon a variable area sound track which is symmetrical aboutits vertical center line, and whose undivided transparent portion variesin width; and wherein light fiux emanating from said uniformlyilluminated light spot is, in the vertical plane, focused at a positionand, in the horizontal plane, difiused at said position, whereby a lightspot of vertically varying illumination is formed at said position; andwherein. lightfiux emanating from said light spot of vertically varyingillumination effects the exposure of a positive film when said positivefilm moves vertically through a second plane, whereby a variable densitysound track having a light transmission is produced on said positivefilm; the provision of means defining the height of said uniformlyilluminated light spot: said defining means including a screen with anopening having a vertical center line and two horizontal edges, saidhorizontal edges being at" a distance from one another, and at least oneof said horizontal edges being curved in such a manner that saiddistance varies in linear relation to the slope of a curve representinga relationship between said width of said transparent portion and saidexposure of said positive film which results in a non-linearrelationship between said width and said light transmission of saidvariable density sound track after said positive film has beendeveloped, said non-linear relationship being such that, when a print ismade of said variable density sound track, the light transmission ofsaid print after development thereof is substantially linearly relatedto said width;

said horizontal edges being so disposed with respect to said lastmentioned center line that said last mentioned center line is equal tosaid dismoves through said first plane.

horizontal edges, said horizontal edges being at l a. distance from oneanother, and at least one of said horizontal edges being curved in sucha manner that said distance varies in linear relation to the slope of acurve representing a relationship between said width of said transparentportion and said exposure of said positive film which rewhosetransparent portion varies in width; and

wherein light fiux emanating from said uniformfly illuminated light spotis, in the vertical plane.

focused at a position and, in the horizontal plane, diffused at saidposition, whereby a light spot of vertically varying illumination isformed at said position; and wherein lightflux emanating from said lightspot of vertically varying illumination effects the exposure of apositive film when said positive film moves vertically through a secondplane, whereby a variable density sound track having a lighttransmission is produced on said positive film; the provision of meansdefining the height of said uniformly illuminated light spot: saiddefining means including a screen with an opening having a verticalcenter line and a height, and said height of said opening varying in thesame sense on both sides of said last mentioned center line and inlinear relation to the slope of a curve representing a relationshipbeuniformly illuminated light spot in such a manner that said uniformlyilluminated light spot has a vertical center line which is in alignmentwith said first mentioned center line when said negative film movesthrough said first plane.

14. In a printing optical system wherein a through a first plane, saidnegative film having thereon a variable area sound track which issymmetrical about its vertical center line, and

whose transparent portion varies in width; and

wherein light flux emanating from said uniformly illuminated light spotis, in the vertical plane, focused at a position and, in the horizontalplane, difiused at said position, whereby a light spot of verticallyvarying illumination is formed at said position; and wherein light fluxemanating -ing a vertical center line and a height, and said height ofsaid opening varying in the same sense on both sides of said lastmentioned center line and in-linear relation to the slope of a curverepresenting a non-linear relationship between said uniformlyilluminated light spot is more or less obscured when a negative filmmoves vertically width of said transparent portion and said exposure ofsaid positive film; said opening being symmetrical about said lastmentioned center line and defining said uniformly illuminated, lightspot in such a manner that said uniformly illuminated light spot has avertical center line which is in alignment with said first mentionedcenter line when saidnegative film moves through, said first plane.

JOHN A. MAURER, JR.

